A transistor is an electrical device which has an adaptable transfer characteristic such that a signal may be amplified or switched. In a wider sense also a transistor can be seen as a diode if, e.g., its base is left floating. A diode has an asymmetric transfer characteristic. So, a diode may be used for conducting a current in a forward direction and for blocking a current in a reverse direction. A frequently used diode is a semiconductor diode, which comprises two different semiconductor materials of opposite conductive type so that a pn-junction is formed between the two materials. By varying the semiconductor materials the transfer characteristic may be adjusted. Often semiconductor diodes have a nonlinear current-voltage characteristic such that same may be used to regulate voltages or to protect circuits.
For example, a transient voltage suppressor diode is used for protecting a circuit from high voltage surges. Such a transient voltage suppressor diode, also referred to as avalanche diode, is designed to go through avalanche breakdown (in the reverse direction) at a specific reverse bias voltage. The time difference between the point of time of the high voltage surge and the avalanche breakdown is called turn on time. Transient voltage suppressor diodes or, in general, electrical devices are often optimized regarding its turn on time.